This is a mechanism module, not a specific disease. Its nodes are successive steps of pathological cytokine receptor-JAK-STAT activation (lesion/ligand drive -> constitutive JAK activity -> constitutive STAT activation -> sustained target-gene transcription -> proliferation and chronic inflammation), with SOCS feedback loss as a parallel entry into the effector node.
Key conformance target (the disorder-agnostic, rate-limiting node): `jak_stat_pathway_activation#Constitutive STAT Activation and Nuclear Translocation`. Attach here when the entry evidences ligand-independent or constitutive STAT phosphorylation, whatever the upstream lesion. Attach at `#Constitutive JAK Kinase Activation` instead when the evidenced lesion is in a Janus kinase itself (JAK2 V617F, activating JAK1 alleles, JAK fusions) and reserve `#Activating Lesion or Sustained Ligand Drive Upstream of JAK` for receptor-level or ligand-excess entries.
Paralog substitution: module nodes list the family members that carry the step; a conforming disorder node narrows `genes` to the paralog its own evidence supports (Polycythemia_Vera -> JAK2; Chronic_Mucocutaneous_Candidiasis -> STAT1; STAT6_Gain_of_Function_Disease -> STAT6). Listing several paralogs on a module node asserts that each can occupy that step, not that any one of them is required. Note that JAK3 appears here only in the four-paralog census of the JAK node: human JAK3 disease is loss-of-function (SCID) and belongs to the deficiency arm, so a JAK3 entry should not conform to these activation nodes.
Straddling diseases. A single disease may have one node on each arm, and the arms must be kept apart at node granularity rather than at entry granularity. SOCS1_Haploinsufficiency is the worked example: losing the SOCS brake raises STAT1 phosphorylation to a degree comparable with STAT1 gain-of-function disease while LOWERING STAT3 phosphorylation, so its `Cytokine Hypersensitivity with Increased STAT Activation` and `Loss of JAK-STAT Negative Feedback` nodes conform here, and its sibling `Reduced STAT3 Phosphorylation` node deliberately does not.
Biological scale. A conforming node need NOT carry the same `biological_scale` as the module node it attaches to, and a divergence is not drift. The module tags its JAK and STAT nodes MOLECULAR because they name protein-level events, whereas a conformer that evidences the same step through a patient-cell readout is properly CELLULAR - as SOCS1_Haploinsufficiency's `Cytokine Hypersensitivity with Increased STAT Activation` node is, being a statement about patient lymphocyte responses. Pick the scale of the claim the entry actually makes, not the module's.
Scope discipline. Merely elevated cytokine signalling is not this module. Conformance requires evidence of constitutive or ligand-independent pathway activity - an activating lesion, a demonstrated ligand-independent phosphorylation readout, or a documented loss of the SOCS brake. A node curated only as "cytokine signalling is increased" (GO:0019221, modifier INCREASED) does not by itself satisfy the module, and should stay unconformed until the constitutive character is evidenced. This distinction matters because roughly 30 KB entries currently annotate GO:0007259 with modifier INCREASED, and only some of them are making the stronger claim.
This is deliberately NOT an Xogenesis module: the terminal output is a dysregulated signalling state, not the formation of a pathological material anatomical entity, so no OGMS/MPATH anchor stanza applies.
In disorder entries that curate increased JAK-STAT signalling without an activating JAK or STAT lesion, is the constitutive signal driven by sustained upstream ligand drive or by failure of SOCS-mediated negative feedback, and what evidence would distinguish them?
KNOWLEDGE GAP
OPEN
gap_jak_stat_socs_feedback_underdetermined
Attached to:
Loss of SOCS-Mediated Negative Feedback
A stuck accelerator and a failed brake produce the same readout - persistent STAT tyrosine phosphorylation - but imply different therapeutic logic, since ligand-directed biologics act only on the former. Across the dismech KB the SOCS arm is almost entirely uncurated: only three disorder entries mention SOCS at all, and only SOCS1_Haploinsufficiency models the brake itself, against roughly thirty entries that annotate GO:0007259 with modifier INCREASED. That asymmetry is a curation gap rather than a biological finding, and it means that for most entries the KB currently cannot answer which route is meant. Conforming entries should not assert SOCS feedback loss without direct evidence (loss of SOCS induction, SOCS promoter silencing, or a lesion shown to escape SOCS control); absent that evidence the entry should conform to the JAK or STAT nodes and leave this node unconformed.
Activating Lesion or Sustained Ligand Drive Upstream of JAK
trigger
The initiating event that commits the axis to constitutive signalling. Three non-exclusive routes converge here: a somatic or germline activating variant in a cytokine receptor (MPL W515 in the myeloproliferative neoplasms, CRLF2 rearrangement in B-lymphoblastic leukaemia), a rearrangement creating a constitutively dimerized kinase fusion, or sustained excess of a cytokine ligand acting on an intact receptor (IL-6 in idiopathic multicentric Castleman disease, IFN-gamma and IL-15 in alopecia areata). The routes are mechanistically distinct upstream but are indistinguishable from the JAK node downwards, which is why they are modelled as one trigger. Conforming disorder nodes substitute the specific receptor or ligand.
Downstream
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Constitutive JAK Kinase Activation
A receptor lesion, kinase fusion, or sustained ligand excess holds the receptor-associated Janus kinases in an activated state, converting a normally transient signal into a continuous one.
Show evidence (1 reference)
"Genetic mutations and polymorphisms are functionally relevant to a variety of human diseases, especially cancer and immune-related conditions."
Establishes that lesions in this pathway are the initiating events in a broad class of human cancer and immune disease, which is what this trigger node represents. Evidence source is OTHER as this is a review article.
Constitutive JAK Kinase Activation
amplifier
Receptor-associated Janus kinases are held in a catalytically active state independent of, or hypersensitive to, ligand. In the physiological pathway ligand engagement activates the receptor-associated JAKs, which transphosphorylate each other and the receptor tail to create STAT docking sites; in disease that step becomes constitutive. The canonical lesion is JAK2 V617F in the JH2 pseudokinase domain, which releases autoinhibition of the adjacent kinase domain; activating JAK1 alleles produce the analogous state in immune dysregulatory disease. Four Janus kinases occupy this step (JAK1, JAK2, JAK3, TYK2) and pair selectively with different receptor chains, which is what gives JAK-selective inhibitors their differing clinical profiles. This node is the JAK-inhibitor drug target.
Downstream
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Constitutive STAT Activation and Nuclear Translocation
Continuously active JAKs phosphorylate STAT transcription factors docked at the receptor, driving STAT activation without a ligand signal.
Show evidence (3 references)
"Upon engagement by ligand, receptor-associated Janus Kinases (Jaks) become activated and phosphorylate both each other and the intracellular tail of their receptors, thereby creating docking sites for latent, cytoplasmic transcription factors termed signal transducers and activators of..."
Defines the normal kinase step that becomes constitutive in this node, and the mechanism by which activated JAKs create the STAT docking sites that drive the downstream effector. Evidence source is OTHER as this is a review article.
"There are four Jaks, Jak1, Jak2, Jak3, and Tyk2, which selectively bind different receptor chains"
Grounds the four-paralog gene list on this node and the selective receptor pairing that conforming entries narrow to. Evidence source is OTHER as this is a review article.
"The mutation, a valine-to-phenylalanine substitution at amino acid position 617, leads to constitutive tyrosine phosphorylation activity that promotes cytokine hypersensitivity"
The archetypal lesion for this node: JAK2 V617F confers constitutive tyrosine kinase activity and cytokine hypersensitivity, the defining properties of constitutive JAK activation. The quote is trimmed to the cell-based arm of this sentence and typed IN_VITRO; the in vivo murine arm of the same sentence is cited separately, and with its own evidence_source, on the consequence node.
Constitutive STAT Activation and Nuclear Translocation
central effector
The rate-limiting, disorder-agnostic node of the module and its key conformance target. STAT transcription factors are tyrosine-phosphorylated, dimerize, and translocate to the nucleus continuously rather than transiently. Every upstream route in this module converges here, and a gain-of-function STAT allele enters at this node directly, without any upstream receptor or kinase lesion. Seven mammalian STATs exist; the four listed here are those with established human gain-of-function disease (STAT1 in chronic mucocutaneous candidiasis, STAT3 in the GOF immune dysregulation syndrome, STAT5B in overgrowth, STAT6 in severe allergic disease). Conforming disorder nodes narrow to the paralog their own phospho-STAT or genetic evidence supports.
Downstream
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Sustained STAT-Driven Target-Gene Transcription
Persistently nuclear STAT dimers occupy their genomic binding sites continuously, converting a transient transcriptional response into a sustained program.
Show evidence (3 references)
"Jak-mediated phosphorylation activates STATs, which in turn directly bind DNA and regulate gene expression"
Establishes the STAT activation step this node represents and its direct coupling to gene regulation, which is the downstream edge. Evidence source is OTHER as this is a review article.
"Seven mammalian STAT family members have been identified (STAT1, STAT2, STAT3, STAT4, STAT5a, STAT5b, STAT6)."
Grounds the STAT paralog census behind this node's gene list, from which conforming entries select the disorder-specific family member. Evidence source is OTHER as this is a review article.
"dysregulation of this pathway is a central pathogenic component in myelofibrosis regardless of the mutational status of JAK2"
Supports treating constitutive pathway activation, rather than any single upstream lesion, as the rate-limiting node: myelofibrosis converges here whether or not JAK2 itself is mutated.
Sustained STAT-Driven Target-Gene Transcription
effector
Continuously nuclear STAT dimers drive a sustained transcriptional program rather than a self-limiting one. STATs bind tens of thousands of genomic sites and regulate thousands of protein-coding genes plus microRNAs and long non-coding RNAs, and they reshape chromatin and enhancer landscapes, so the downstream output is a broad change of cell state rather than a small set of induced genes. In conforming entries this node is where the disorder-specific output program is named: an interferon-stimulated gene signature, a Th17-skewing program, or a proliferative and anti-apoptotic program.
Downstream
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Cytokine-Independent Proliferation and Chronic Inflammation
A sustained STAT transcriptional program removes the cytokine dependence of proliferation and maintains an inflammatory output that does not resolve.
Show evidence (2 references)
"It is now clear that STATs bind tens of thousands of sites in the genome and regulate transcription of thousands of protein-coding genes, along with microRNAs and long non-coding RNAs."
Establishes the breadth of the STAT transcriptional output that this node represents, and why sustained STAT activity produces a change of cell state rather than a narrow gene response. Evidence source is OTHER as this is a review article.
"STATs also have important impacts on chromatin structure and the distinctive enhancer landscapes of differentiating cells."
Supports the chromatin and enhancer remodelling component of this node, which is why the downstream consequence is a durable phenotypic program. Evidence source is OTHER as this is a review article.
Cytokine-Independent Proliferation and Chronic Inflammation
consequence
The terminal output of the module. Cells acquire growth-factor independence or hypersensitivity and proliferate without the normal cytokine requirement, while the same sustained transcriptional program maintains a chronic inflammatory state. Which arm dominates is disorder-specific: clonal myeloproliferation in the myeloproliferative neoplasms and lymphoid malignancies, chronic autoinflammation and tissue infiltration in the monogenic immune dysregulation syndromes, and organ-specific inflammatory disease in the autoimmune conformers. Conforming entries substitute their own proliferative or inflammatory endpoint.
Show evidence (2 references)
"Myeloproliferative disorders are clonal haematopoietic stem cell malignancies characterized by independency or hypersensitivity of haematopoietic progenitors to numerous cytokines."
Names the defining property of this terminal node - proliferation that no longer depends on the normal cytokine signal - in the archetypal disease class for the module.
"promotes cytokine hypersensitivity and induces erythrocytosis in a mouse model"
In vivo demonstration that the constitutive kinase lesion is sufficient to produce the proliferative endpoint of this node, not merely correlated with it. Typed MODEL_ORGANISM because the causal step is shown in mouse; the cell-based arm of the same sentence is cited separately on the JAK node.
Janus Kinase Inhibitor Therapy
Platform:
Small molecule
Small-molecule ATP-competitive inhibitors of the Janus kinases (ruxolitinib, baricitinib, tofacitinib, upadacitinib, fedratinib, and JAK-selective agents such as ritlecitinib and deuruxolitinib) block the catalytic step at the Constitutive JAK Kinase Activation node and thereby suppress the downstream STAT effector. This is the module's drug-target design pattern: a conforming disorder entry links its JAK inhibitor by target_mechanisms to the specific node the drug acts on, rather than to a downstream symptom. Because the four JAKs pair selectively with different receptor chains, agents differ in which cytokine families they suppress, and a conforming entry should name the inhibitor actually evidenced for that disease rather than inheriting this generic class entry.
Evidence: 2